1. Field of the Invention
The present invention relates to recombinant pro-cobra venom factor (proCVF), DNA encoding recombinant proCVF, plasmids comprising such DNA, and transformed microorganisms containing such DNA. The present invention also relates to various methods of making and using recombinant proCVF.
2. Discussion of the Background
The third component of complement, C3, plays a pivotal role in both the classical and alternative pathways of complement activation, and many of the physiologic C3 activation products have important functions in the immune response and host defense (Muller-Eberhard, H. J., 1988, Annu. Rev. Biochem. 57:321). In the alternative pathway, the activated form of C3, C3b, is a structural subunit of the C3 convertase. This bimolecular enzyme consists of C3b and Bb, the activated form of factor B. This enzyme is formed by the binding of C3b to factor B that is subsequently cleaved by factor D, resulting in the formation of the C3 convertase, C3b,Bb, and the release of the activation peptide Ba. The C3 convertase activates C3 by cleaving the molecule into C3b and the anaphylatoxin, C3a. The C3b molecule will bind in close proximity to the C3 convertase. Eventually, the bound C3b will allow for the activation of CS into C5b and the anaphylatoxin, C5a. C5 activation occurs by the same C3b,Bb enzyme that can cleave C5 when it is bound to an additional C3b molecule. The C5-cleaving enzyme is called C5 convertase. It is a trimolecular complex composed of (C3b).sub.2,Bb. Inasmuch as the activation of both C3 and C5 occurs at the identical active site in the Bb subunit, the enzyme is also called C3/C5 convertase; and only one EC number has been assigned (EC 3.4.21.47).
Cobra venom contains a structural and functional analog of C3 called cobra venom factor (CVF). This molecule can bind factor B in human and mammalian serum to form the complex, CVF,B (Hensley, P. M., et al, 1986, J. Biol. Chem. 261:11038), which is also cleaved by factor D into the bimolecular enzyme CVF,Bb and Ba (Vogel. C. -W., et al, 1982, J. Biol. Chem. 257:8292). The bimolecular complex CVF,Bb is a C3/C5 convertase that activates C3 and C5 analogously to the C3/C5 convertase formed with C3b (Vogel, C. -W., 1991, In Handbook of Natural Toxins, Vol. 5, Reptile and Amphibian Venoms. A. T. Tu, ed. Marcel Dekker, New York, p. 147). Although the two C3/C5 convertases C3b,Bb and CVF,Bb share the molecular architecture, the active site-bearing Bb subunit, and the substrate specificity, the two enzymes exhibit significant functional differences. The CVF,Bb enzyme is physicochemically far more stable than C3b,Bb (Vogel. C. -W., et al, 1982, J. Biol. Chem. 257:8292; Medicus, R. G., et al, 1976, J. Exp. Med. 144:1076), it is resistant to inactivation by the regulatory proteins factors H and 1 (Lachmann, P. J., et al, 1975, Clin. Exp. Immunol. 21:109; Nagaki, K., et al, 1978, Int. Arch. Allergy Appl. Tmmunol. 57:221), it exhibits different kinetic properties (Vogel. C. -W., et al, 1982, J. Biol. Chem. 257:8292; Pangburn, M. K., et al, 1986, Biochem J. 235:723), and it does not require additional C3b for C5 cleavage (Miyama, A., et al, 1975, Biken J. 18:193; Von Zabern, et al, 1980, Immunobiology 157:499). CVF and mammalian C3 have been shown to exhibit several structural similarities including immunologic cross-reactivity (Alper, C. A. et al, 1983, Science 191:1275; Eggertsen, G. A., et al, 1983, J. Immunol. 131:1920; Vogel, C. -W., et al, 1984, J. Immunol. 133:3235; Grier, A. H., et al, 1987, J. Immunol. 139:1245), amino acid composition (Vogel, C. -W., et al, 1984, J. Immunol. 133:3235; Vogel, C. -W., et al, 1985, Complement 2:81), circular dichroism spectra, and secondary structure (Vogel, C. -W., et al, 1984, J. Immunol. 133:3235), electron microscopic ultrastructure (Vogel, C. -W., et al, 1984, J. Immunol. 133:3235; Smith, C. A., et al, 1982, J. Biol. Chem. 257:9879; Smith, C. A., et al, 1984, J. Exp. Med. 159:324), and amino-terminal amino acid sequence (Vogel, C. -W., et al, 1984, J. Immunol. 133:3235; Lundwall, A., et al, 1984, FEBS Lett. 169:57). Nevertheless, significant structural differences exist between the two molecules. Whereas C3 is a two-chain molecule with an apparent molecular mass, dependent on the species, of 170 to 190 kDa (Eggertsen, G. A., et al, 1983, J. Immunol. 131:1920; DeBruijn, M. H. L., et al, 1985, Proc. Natl. Acad. Sci. USA 82:708; Alsenz, J., et al, 1992, Dev. Comp. Immunol. 16:63; Vogel, C. -W., et al, 1984, Dev. Comp. Immunol. 8:239), CVF is a three-chain molecule with an apparent molecular mass of 149 kDa (Vogel, C. -W., et al, 1984, J. Immunol. Methods 73:203) that resembles C3c, one of the physiologic activation products of C3 (Vogel, C. -W., 1991, In Handbook of Natural Toxins, Vol. 5, Reptile and Amphibian Venoms. A. T. Tu, ed. Marcel Dekker, New York, p. 147; Vogel, C. -W., et al, 1984, J. Immunol. 133:3235). Another significant structural difference between C3 and CVF lies in their glycosylation, CVF has a 7.4% (w/w) carbohydrate content consisting mainly of N-linked complex-type chains with unusual .alpha.-galactosyl residues at the non-reducing termini (Vogel, C. -W., et al, 1984, J. Immunol. Methods 73:203; Gowda, D. C., et al, 1992, Mol. Immunol. 29:335). In contrast, human and rat C3 exhibit a lower extent of glycosylation with different structures of their oligosaccharide chains (Hase, S., et al, 1985, J. Biochem. 98:863; Hirani, S., et al, 1986, Biochem. J. 233:613; Miki, K., et al, 1986, Biochem J. 240:691).
The multifunctionality of the C3 protein, which interacts specifically with more than 10 different plasma proteins or cell surface receptors, has spurred significant interest in a detailed structure/function analysis of the molecule. For some ligands of C3 the binding sites have been assigned to more or less defined regions of the C3 polypeptide including factor H (Ganu, V. S., et al, 1985, Complement 2:27), properdin (Daoudaki, M. E., et al, 1988, J. Immunol. 140:1577; Farries, T. C., et al, 1990, Complement Inflamm. 7:30), factor B (Fishelson, Z., 1981, Mol. Immunol. 28:545), and the complement receptors CR1 (Becherer, J. D., et al, 1988, J. Biol. Chem. 263:14586), CR2 (Lambris, J. D., et al, 1985, Proc. Natl. Acad. Sci. USA 82:4235; Becherer, J. D., et al, 1989, Curr. Top. Microbiol. Immunol. 153:45), and CR3 (Becherer, J. D., et al, 1989, Curr. Top. Microbiol. Immunol. 153:45; Wright, S. D., et al, 1987, Proc. Natl. Acad. Sci. USA 84:1965; Taniguchi-Sidle, A., et al, 1992, J. Biol. Chem. 267:635). The elucidation of structural differences between C3 and CVF, two closely related molecules that share some properties (e.g., formation of a C3/C5 convertase) but differ in others (e.g., susceptibility to regulation by factors H and I) can be expected to help identify functionally important regions of the C3 molecule.
The inventors have recently discovered that CVF actually exists in two forms, CVF1 and CVF2. It is desirable to obtain large quantities of CVF1 and CVF2 for a number of reasons. However, the isolation of large quantities of the peptides from cobras is problematic to say the least. Thus, it is desirable to clone the genes which encode CVF1 and CVF2. It is also desirable to provide molecules that exhibit the activity of CVF and can be conveniently produced in large quantities.